Electrode design for electrochromic devices

ABSTRACT

An electrochromic device, such as a window or mirror, is disclosed that includes first and second substrates each having an inner surface spaced apart from one another to define a chamber, first and second electrodes carried on the inner surface of the second substrate and disposed thereon to be electrically isolated from one another, and an electrochromic medium disposed in the chamber. The electrodes may be disposed on the inner surface of the second substrate in substantially co-planar relation. Alternatively, the electrodes may be arranged in a stacked relation, with a layer of dielectric material provided therebetween.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/343,345, entitled “ELECTRODE DESIGN FOR ELECTROCHROMICDEVICES,” filed on Jun. 30, 1999, by Thomas F. Guarr et al., the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention generally relates to devices of reversiblyvariable transmittance to electromagnetic radiation. More specifically,the present invention relates to an improved electrode design forelectrochromic light filters and mirrors.

[0003] Devices of reversibly variable transmittance to electromagneticradiation have been proposed as the variable transmittance element invariable transmittance light filters, variable reflectance mirrors, anddisplay devices, which employ such light filters or mirrors in conveyinginformation. These variable transmittance light filters have includedarchitectural windows, skylights, and windows and sunroofs forautomobiles.

[0004] Devices of reversibly variable transmittance to electromagneticradiation, wherein the transmittance is altered by electrochromic means,are described, for example, by Chang, “Electrochromic andElectrochemichromic Materials and Phenomena,” in Non-emissiveElectrooptic Displays, A. Kmetz and K. von Willisen, eds. Plenum Press,New York, N.Y. 1976, pp. 155-196 (1976) and in various parts ofElectrochromism, P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCHPublishers, Inc., New York, N.Y. (1995). Numerous electrochromic devicesare known in the art. See, e.g., U.S. Pat. No. 3,451,741 issued toManos; U.S. Pat. No. 4,090,358 issued to Bredfeldt et al.; U.S. Pat. No.4,139,276 issued to Clecak et al.; U.S. Pat. No. 3,453,038 issued toKissa et al.; U.S. Pat. Nos. 3,652,149, 3,774,988, and 3,873,185 issuedto Rogers; and U.S. Pat. Nos. 3,282,157, 3,282,158, 3,282,160, and3,283,656 issued to Jones et al.

[0005] In addition to these devices, there are commercially availableelectrochromic devices and associated circuitry, such as those disclosedin U.S. Pat. No. 4,902,108, entitled “SINGLE-COMPARTMENT, SELF-ERASING,SOLUTION-PHASE ELECTROCHROMIC DEVICES, SOLUTIONS FOR USE THEREIN, ANDUSES THEREOF,” issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No.1,300,945, entitled “AUTOMATIC REARVIEW MIRROR SYSTEM FOR AUTOMOTIVEVEHICLES,” issued May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No.5,128,799, entitled “VARIABLE REFLECTANCE MOTOR VEHICLE MIRROR,” issuedJul. 7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled“ELECTRO-OPTIC DEVICE,” issued Apr. 13, 1993, to H. J. Byker et al.;U.S. Pat. No. 5,204,778, entitled “CONTROL SYSTEM FOR AUTOMATIC REARVIEWMIRRORS,” issued Apr. 20, 1993, to J. H. Bechtel; U.S. Pat. No.5,278,693, entitled “TINTED SOLUTION-PHASE ELECTROCHROMIC MIRRORS,”issued Jan. 11, 1994, to D. A. Theiste et al.; U.S. Pat. No. 5,280,380,entitled “UV-STABILIZED COMPOSITIONS AND METHODS,” issued Jan. 18, 1994,to H. J. Byker; U.S. Pat. No. 5,282,077, entitled “VARIABLE REFLECTANCEMIRROR,” issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376,entitled “BIPYRIDINIUM SALT SOLUTIONS,” issued Mar. 15, 1994, to H. J.Byker; U.S. Pat. No. 5,336,448, entitled “ELECTROCHROMIC DEVICES WITHBIPYRIDINIUM SALT SOLUTIONS,” issued Aug. 9, 1994, to H. J. Byker; U.S.Pat. No. 5,434,407, entitled “AUTOMATIC REARVIEW MIRROR INCORPORATINGLIGHT PIPE,” issued Jan. 18, 1995, to F. T. Bauer et al.; U.S. Pat. No.5,448,397, entitled “OUTSIDE AUTOMATIC REARVIEW MIRROR FOR AUTOMOTIVEVEHICLES,” issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No.5,451,822, entitled “ELECTRONIC CONTROL SYSTEM,” issued Sep. 19, 1995,to J. H. Bechtel et al. Each of these patents is commonly assigned withthe present invention and the disclosures of each, including thereferences contained therein, are hereby incorporated herein in theirentirety by reference. Such electrochromic devices may be utilized in afully integrated inside/outside rearview mirror system for a vehicle oras separate inside or outside rearview mirror systems.

[0006] It is desirable to use reversibly variable transmittance lightfilters in architectural windows, skylights, and in windows and sunroofsfor automobiles in order to reduce the transmittance of the filter withrespect to direct or reflected sunlight during daytime, while notreducing such transmittance during nighttime. Not only do such lightfilters reduce bothersome glare and ambient brightness, they also reducefading and generated heat caused by the transmittance of sunlightthrough the window.

[0007] Variable transmission electrochromic devices such as windows andlight filters typically include a structure similar to that shown inFIG. 1. Specifically, they typically include first and secondtransparent substrates 12 and 14, which are commonly made of glass andarranged in parallel, spaced-apart relation. The electrochromic devicesalso typically include first and second transparent, electricallyconductive layers forming electrodes 16 and 18 provided on theinterfacing surfaces of substrates 12 and 14. A seal 20 is provided tosecure the coated substrates together and to provide a chamber 22between the coated substrates in which an electrochromic medium 24 isprovided. Electrically conductive clips 26 and 28 are respectivelyattached to one of the coated substrates so as to be electricallycoupled to one of electrode layers 16 and 18. The electrochromic medium24 is contained in chamber 22. The electrochromic medium 24 is in directcontact with transparent electrode layers 16 and 18, through whichpasses electromagnetic radiation whose intensity is reversibly modulatedin the device by a variable voltage or potential applied to electrodelayers 16 and 18 through clip contacts 26 and 28 and an electroniccircuit (not shown).

[0008] The electrochromic medium 24 includes two different coloringspecies—a cathodic species and an anodic species, which are colorless ornearly colorless in an inactivated state. In most cases, when there isno electrical potential difference between transparent electrodes 16 and18, the electrochromic medium 24 in chamber 22 is colorless or nearlycolorless, and incoming light (I_(o)) enters through second substrate14, passes through transparent electrode 18, electrochromic containingchamber 22, transparent electrode 16, and first substrate 12. When apotential difference is applied between transparent electrodes 16 and 18at the cathode, the cathodic species are reduced (i.e., accept electronsfrom the cathode). On the other hand, the anodic species are oxidized atthe anode (i.e., donate electrons to anode 16). As the cathodic andanodic species in electrochromic medium 24 accept and donate electronsfrom/to electrodes 18 and 16, respectively, at least one of the speciesbecomes colored. The anodic and cathodic species in medium 24 return toa colorless or nearly colorless state once they exchange electrons inthe center portion of chamber 22. Nevertheless, so long as a sufficientpotential is applied across electrodes 16 and 18, there is a sufficientamount of the anodic and cathodic species that are oxidized and reducedso as to color an electrochromic cell. Because the anodic and cathodicspecies exchange electrons in the center portion of chamber 22 anddonate and accept electrons when adjacent a respective electrode 16 and18, the reduced cathodic component contributing to the perceived colorexists primarily adjacent cathode 18, and the oxidized anodic componentexists proximate to anode 16. This also corresponds to the fact that theconcentration of reduced cathodic species is greatest proximate cathode18, and the concentration of oxidized anodic species is greatestadjacent anode 16.

[0009] Commercially available electrochromic media that are suitable foruse in chamber 24 generally include solution-phase and solid-stateelectrochromic materials. In an all solution-phase medium, theelectrochemical properties of the solvent, optional inert electrolyte,anodic materials, cathodic materials, and any other components thatmight be present in the solution are preferably such that no significantelectrochemical or other changes occur at a potential difference whichoxidizes anodic material and reduces the cathodic material other thanthe electrochemical oxidation of the anodic material, electrochemicalreduction of the cathodic material, and the self-erasing reactionbetween the oxidized form of the anodic material and the reduced form ofthe cathodic material.

[0010] Electrode layers 16 and 18 are connected to electronic circuitrywhich is effective to electrically energize the electrochromic medium,such that when a potential is applied across the transparent electrodes16 and 18, electrochromic medium 24 in chamber 22 darkens, such thatincident light (I_(o)) is attenuated as the light passes through theelectrochromic device. By adjusting the potential difference between thetransparent electrodes, such a device can function as a “gray-scale”device, with continuously variable transmittance over a wide range. Forsolution-phase electrochromic systems, when the potential between theelectrodes is removed or returned to zero, the device spontaneouslyreturns to the same zero-potential, equilibrium color and transmittanceas the device had before the potential was applied.

[0011] Another common construction for an electrochromic device is shownin FIG. 2. In the construction shown in FIG. 2, the first and secondtransparent substrates 12 and 14 are arranged in a parallel,spaced-apart relationship in the same manner as the electrochromicdevice shown in FIG. 1. Also, a seal 20 is provided between substrates12 and 14 so as to provide a sealed chamber 22 lying therebetween. Theelectrochromic device shown in FIG. 2 differs from that shown in FIG. 1in that electrochromic medium 24 is solid-state rather than asolution-phase and is formed within a multi-layer stack, with anelectrolyte material layer 30 adjacent electrochromic layer 24 betweenfirst and second transparent electrode layers 16 and 18. This stack iscarried on the inner surface of one of first and second substrates 12and 14, with either gas or air surrounding the stack within chamber 22.As will be described further below, the electrochromic device shown inFIG. 2 is susceptible to many of the same problems as the electrochromicdevice shown in FIG. 1.

[0012] Electrochromic devices of the type described above aresusceptible to irreversible damage from ultraviolet (UV) radiation whenoperating in its low transmission state. More specifically, the anodicand cathodic species in electrochromic medium 24 can be adversely andpermanently affected by the UV light emitted by the sun when they are intheir colored states. When the species are not in their colored states,they are generally not adversely affected by UV radiation. The UVabsorption problem has made it impractical to use electrochromic lightfilters in window applications where it is desired to darken windowsduring daytime hours. To minimize the adverse impact of UV radiation onthe electrochromic medium, UV absorbers are often introduced into theelectrochromic medium. These absorbers absorb the UV radiation so as tominimize the amount of UV radiation that is absorbed by the anodic andcathodic species within the electrochromic medium. Such UV radiationabsorbers, however, are not as effective when the electrochromic deviceis darkened, because of the fact that the colored species tend to beconcentrated adjacent to anode 16 and cathode 18 and because thesecolored species thus tend to absorb the UV radiation before the UVabsorber can absorb the UV radiation.

[0013] An additional problem with implementing electrochromic devices inwindows is that the amount of current drawn by the type ofelectrochromic devices shown in FIGS. 1 and 2 is fairly substantial whenthe electrochromic devices are in their colored states. Also, colorbands, or segregation, is known for devices colored for prolongedperiods of time. These problems become very significant whenelectrochromic light filters are utilized in all the windows of a largebuilding.

[0014] Yet another practical problem that arises when utilizingelectrochromic light filters in architectural windows as well as otherforms of windows is that such electrochromic devices are typically madewith a relatively large cell spacing between the substrates in order toobtain uniform color throughout the electrochromic medium. Anyvariations in the distance between the anode and the cathode layersresults in variations in color in the electrochromic medium. Temperedglass substrates are generally not very flat. Thus, when tempered glassis used for substrates 12 and/or 14, the need to create a thick cell ina window becomes more important.

SUMMARY OF THE INVENTION

[0015] Accordingly, it is an aspect of the present invention to overcomethe above-noted problems associated with implementing an electrochromicdevice as a variable transmittance light filter. More specifically, itis an aspect of the present invention to provide an electrochromicdevice that is less susceptible to damage from UV radiation. Anotheraspect of the present invention is to provide an electrochromic devicethat draws less operating current. Another aspect of the presentinvention is to provide an electrochromic device that is less likely tobe affected by surface variations in the transparent substrates thatdefine the chamber in which the electrochromic medium is disposed.

[0016] To achieve these and other aspects and advantages, theelectrochromic device of the present invention comprises a transparentfirst substrate having an outer surface and an inner surface, a secondsubstrate having an inner surface spaced apart from the inner surface ofthe first substrate so as to define a chamber therebetween, a firstelectrode carried on the inner surface of the second substrate, and asecond electrode also carried on the inner surface of the secondsubstrate such that the second electrode is electrically isolated fromthe first electrode. The electrochromic device further includes anelectrochromic medium disposed in the chamber between the inner surfaceof the first substrate and the inner surface of the second substrate,which carries the first and second electrodes. The first and secondelectrodes may be disposed on the inner surface of the second substrateso as to be substantially co-planar with one another. Alternatively, theelectrodes may be arranged in a stacked configuration, with a layer ofdielectric material provided therebetween. In this alternativeconfiguration, the dielectric layer and the second electrode wouldinclude a plurality of apertures through which the electrochromic mediummay contact the first electrode, which underlies the dielectric andsecond electrode layers.

[0017] To achieve the above and other aspects and advantages, anelectrochromic device may further be constructed in accordance with thepresent invention by having a positive electrode, a negative electrodehaving a surface area different from the surface area of the positiveelectrode, and an electrochromic medium including cathodic and anodicspecies, wherein the ratio of cathodic to anodic species within theelectrochromic medium is a function of the ratio of the surface areas ofthe positive and negative electrodes.

[0018] These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the drawings:

[0020]FIG. 1 is a cross-sectional view of a first conventionalelectrochromic device;

[0021]FIG. 2 is a cross-sectional view of a second conventionalelectrochromic device;

[0022]FIG. 3 is a front perspective view of an electrochromic deviceconstructed in accordance with a first embodiment of the presentinvention;

[0023]FIG. 4 is a cross-sectional view of the first embodiment of thepresent invention taken along line IV-IV of FIG. 3;

[0024]FIG. 5 is a cross-sectional view of the first embodiment of thepresent invention taken along line V-V of FIG. 3;

[0025]FIG. 6 is a front perspective view of an electrochromic deviceconstructed in accordance with a second embodiment of the presentinvention;

[0026]FIG. 7 is a cross-sectional view of the second embodiment of thepresent invention taken along line VII-VII of FIG. 6;

[0027]FIG. 8 is an enlarged cross-sectional view of the area of thesecond embodiment shown in FIG. 7 and designated as VII-VII;

[0028]FIG. 9 is a cross-sectional view of the second embodiment of thepresent invention taken along line IX-IX of FIG. 6;

[0029]FIG. 10 is a front perspective view of an electrochromic deviceconstructed in accordance with a third embodiment of the presentinvention;

[0030]FIG. 11 is a cross-sectional view of the third embodiment takenalong line XI-XI of FIG. 10;

[0031]FIG. 12A is a cross-sectional view of an insulated glass unitincorporating an electrochromic device in accordance with one embodimentof the present invention; and

[0032]FIG. 12B is a cross-sectional view of an insulated glass unitincorporating an electrochromic device in accordance with anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Electrochromic devices have as a component part an electrochromicmedium. Electrochromic devices have been, or can be, used in a varietyof applications wherein the transmitted or reflected light can bemodulated. Such devices include rearview mirrors, such as are used forvehicles; windows for the exterior of a building, home, or vehicle;skylights for buildings including tubular light filters; windows inoffice or room partitions; display devices; contrast enhancement filtersfor displays; light filters for photographic devices and light sensors;and indicators for power cells and batteries.

[0034] An electrochromic device 100 constructed in accordance with afirst embodiment of the present invention is shown in FIGS. 3 through 5(not to scale). Electrochromic device 100 includes a transparent firstsubstrate 114 having an outer surface 114 a and an inner surface 114 b.Device 100 further includes a second substrate 112 having an innersurface 112 b spaced apart from inner surface 114 b of first substrate114. Substrates 112 and 114 are preferably parallel to one another witha seal 120 disposed therebetween to define a chamber 122 betweensubstrates 112 and 114. According to the first embodiment, a firstelectrode 116 and a second electrode 118 are carried on inner surface112 b of second substrate 112. First and second electrodes 116 and 118are electrically isolated from one another by a small gap 117. As shownin FIGS. 3 and 4, first and second electrodes 116 and 118 include aplurality of parallel, substantially co-planar, spaced-apart elongatedstrips (or fingers) 116 a and 118 a of electrically conductive materialthat are interdigitatedly disposed on the inner surface of substrate112.

[0035] As used herein to describe the physical relation of the first andsecond electrodes, the term “substantially co-planar” means that theelectrodes lie in a common plane when the surface they are disposed onis planar, and that at least portions of the electrodes lie in asubstantially common plane along any given tangent when the surface theyare disposed on is non-planar. As also used herein reference to anelectrode being “carried on” a substrate or element, means that theelectrode is disposed directly or indirectly on the substrate orelement.

[0036] Electrochromic device 100 includes an electrochromic medium 124provided within chamber 122. Electrochromic medium 124 includeselectrochromic anodic and cathodic materials that can be grouped intothe following categories:

[0037] Single layer—the electrochromic medium is a single layer ofmaterial which may include small nonhomogeneous regions and includessolution-phase devices where a material is contained in solution in theionically conducting electrolyte and remains in solution in theelectrolyte when electrochemically oxidized or reduced. Solution-phaseelectroactive materials may be contained in the continuoussolution-phase of a cross-linked polymer matrix in accordance with theteachings of U.S. Pat. No. 5,928,572, entitled “ELECTROCHROMIC LAYER ANDDEVICES COMPRISING SAME” or International Patent Application No.PCT/US98/05570 entitled “ELECTROCHROMIC POLYMERIC SOLID FILMS,MANUFACTURING ELECTROCHROMIC DEVICES USING SUCH SOLID FILMS, ANDPROCESSES FOR MAKING SUCH SOLID FILMS AND DEVICES.”

[0038] At least three electroactive materials, at least two of which areelectrochromic, can be combined to give a pre-selected color asdescribed in U.S. Pat. No. 6,020,987 entitled “ELECTROCHROMIC MEDIUMCAPABLE OF PRODUCING A PRE-SELECTED COLOR.”

[0039] The anodic and cathodic materials can be combined or linked by abridging unit as described in International Application No.PCT/WO97/EP498 entitled “ELECTROCHROMIC SYSTEM.” It is also possible tolink anodic materials or cathodic materials by similar methods. Theconcepts described in these applications can further be combined toyield a variety of electrochromic materials that are linked.

[0040] Additionally, a single layer medium includes the medium where theanodic and cathodic materials can be incorporated into the polymermatrix as described in International Application No. PCT/WO98/EP3862entitled “ELECTROCHROMIC POLYMER SYSTEM” or International PatentApplication No. PCT/US98/05570 entitled “ELECTROCHROMIC POLYMERIC SOLIDFILMS, MANUFACTURING ELECTROCHROMIC DEVICES USING SUCH SOLID FILMS, ANDPROCESSES FOR MAKING SUCH SOLID FILMS AND DEVICES.”

[0041] Also included is a medium where one or more materials in themedium undergoes a change in phase during the operation of the device,for example, a deposition system where a material contained in solutionin the ionically conducting electrolyte which forms a layer, or partiallayer on the electronically conducting electrode when electrochemicallyoxidized or reduced.

[0042] Multilayer—the medium is made up in layers and includes at leastone material attached directly to an electronically conducting electrodeor confined in close proximity thereto which remains attached orconfined when electrochemically oxidized or reduced. Examples of thistype of electrochromic medium are the metal oxide films, such astungsten oxide, iridium oxide, nickel oxide, and vanadium oxide. Amedium, which contains one or more organic electrochromic layers, suchas polythiophene, polyaniline, or polypyrrole attached to the electrode,would also be considered a multilayer medium.

[0043] In addition, the electrochromic medium may also contain othermaterials, such as light absorbers, light stabilizers, thermalstabilizers, antioxidants, thickeners, or viscosity modifiers. It isoften desirable in the construction of electrochromic devices toincorporate thinner glass in order to decrease the overall weight of thedevice so that the mechanisms used to manipulate the orientation of thedevice are not overloaded. Decreasing the weight of the device alsoimproves the dynamic stability of the device when exposed to vibrations.Electrochromic mirrors incorporating a solution-phase electrochromicmedium and two thin glass elements suffer from being flexible and areprone to warpage or breakage, especially when exposed to extremeenvironments. This problem is substantially improved by using animproved electrochromic device incorporating two thin glass elementshaving an improved gel material. This improved device is disclosed incommonly assigned U.S. Pat. No. 5,940,201 entitled “ELECTROCHROMICMIRROR WITH TWO THIN GLASS ELEMENTS AND A GELLED ELECTROCHROMIC MEDIUM,”filed on or about Apr. 2, 1997. The entire disclosure, including thereferences contained therein, of this U.S. patent is incorporated hereinby reference. If a specific color is desired for the electrochromicdevice, the composition of the electrochromic medium may beappropriately selected in accordance with the teachings of commonlyassigned U.S. Pat. No. 6,020,987, entitled “ELECTROCHROMIC MEDIUMCAPABLE OF PRODUCING PRE-SELECTED COLOR,” filed on Apr. 2, 1997, by K.L. Baumann et al. and International PCT Application Publication No. WO98/44384, the disclosures of which are incorporated by reference herein.

[0044] First and second transparent substrates 112 and 114 may be anymaterial which is transparent and has sufficient strength to be able tooperate in the environmental conditions to which the device will beexposed. Substrates 112 and 114 may comprise any type of borosilicateglass, soda lime glass, float glass, or any other material, such as, forexample, MYLAR®, polyvinylidene halides, such as polyvinylidenechloride, a polymer or plastic, such as cyclic olefin copolymers likeTopas® available from Ticona, LLC. of Summitt, N.J., that is transparentin the visible region of the electromagnetic spectrum. Substrates 112and 114 are preferably a sheet of glass. If the device of the presentinvention is used as a mirror, first substrate 112 preferably meets theoperational conditions outlined above, except that it does not need tobe transparent, and therefore may comprise polymers, metals, colored ornon-transparent glass, and ceramics.

[0045] Seal member 120 may be any material that is capable of adhesivelybonding the coatings on inner second surface 112 b to inner surface 114b to seal the perimeter, such that electrochromic material 124 does notleak from chamber 122. The performance requirements for a perimeter sealmember 120 used in an electrochromic device are similar to those for aperimeter seal used in a liquid crystal device (LCD), which are wellknown in the art. The seal preferably has good adhesion to glass,metals, and metal oxides; preferably has low permeabilities for oxygen,moisture vapor, and other detrimental vapors and gases; and must notinteract with or poison the electrochromic or liquid crystal material itis meant to contain and protect. The perimeter seal can be applied bymeans commonly used in the LCD industry, such as by silk-screening ordispensing. Totally hermetic seals, such as those made with glass fritor solder glass, can be used, but the high temperatures (usually near450° C.) involved in processing this type of seal can cause numerousproblems, such as glass substrate warpage, changes in the properties oftransparent conductive electrode, and oxidation or degradation of thereflector. Because of their lower processing temperatures,thermoplastic, thermosetting, or UV-curing organic sealing resins arepreferred. Such organic resin sealing systems for LCDs are described inU.S. Pat. Nos. 4,297,401, 4,418,102, 4,695,490, 5,596,023, and5,596,024. Because of their excellent adhesion to glass, low oxygenpermeability, and good solvent resistance, epoxy-based organic sealingresins are preferred. These epoxy resin seals may be UV curing, such asdescribed in U.S. Pat. No. 4,297,401, or thermally curing, such as withmixtures of liquid epoxy resin with liquid polyamide resin ordicyandiamide, or they can be homopolymerized. The epoxy resin maycontain fillers or thickeners to reduce flow and shrinkage, such asfumed silica, silica, mica, clay, calcium carbonate, alumina, etc.,and/or pigments to add color. Fillers pretreated with hydrophobic orsilane surface treatments are preferred. Cured resin crosslink densitycan be controlled by use of mixtures of mono-functional, di-functional,and multi-functional epoxy resins and curing agents. Additives such assilanes or titanates can be used to improve the seal's hydrolyticstability, and spacers such as glass beads or rods can be used tocontrol final seal thickness and substrate spacing. Suitable epoxyresins for use in a perimeter seal member 120 include, but are notlimited to: “EPON RESIN” 813, 825, 826, 828, 830, 834, 862, 10O1F,1002F, 2012, DPS-155, 164, 1031, 1074, 58005, 58006, 58034, 58901, 871,872, and DPL-862 available from Shell Chemical Co., Houston, Tex.;“ARALITE” GY 6010, GY 6020, CY 9579, GT 7071, XU 248, EPN 1139, EPN1138, PY 307, ECN 1235, ECN 1273, ECN 1280, MT 0163, MY 720, MY 0500, MY0510, and PT 810 available from Ciba Geigy, Hawthorne, N.Y.; and“D.E.R.” 331, 317, 361, 383, 661, 662, 667, 732, 736, “D.E.N.” 431, 438,439 and 444 available from Dow Chemical Co., Midland, Mich. Suitableepoxy curing agents include V-15, V-25, and V40 polyamides from ShellChemical Co.; “AJICURE” PN-23, PN-34, and VDH available from AjinomotoCo., Tokyo, Japan; “CUREZOL” AMZ, 2MZ, 2E4MZ, C11Z, C17Z, 2PZ, 2IZ, and2P4MZ available from Shikoku Fine Chemicals, Tokyo, Japan; “ERISYS” DDAor DDA accelerated with U-405, 24EMI, U-410, and U-415 available fromCVC Specialty Chemicals, Maple Shade, N.J.; and “AMICURE” PACM, 352, CG,CG-325, and CG1200 available from Air Products, Allentown, Pa. Suitablefillers include fumed silica such as “CAB-O-SIL” L-90, LM-130, LM-5,PTG, M-5, MS-7, MS-55, TS-720, HS-5, and EH-5 available from CabotCorporation, Tuscola, Ill.; “AEROSIL” R972, R974, R805, R812, R812 S,R202, US204, and US206 available from Degussa, Akron, Ohio. Suitableclay fillers include BUCA, CATALPO, ASP NC, SATINTONE 5, SATINTONESP-33, TRANSLINK 37, TRANSLINK 77, TRANSLINK 445, and TRANSLINK 555available from Engelhard Corporation, Edison, N.J. Suitable silicafillers are SILCRON G-130, G-300, G-100-T, and G-100 available from SCMChemicals, Baltimore, Md. Suitable silane coupling agents to improve theseal's hydrolytic stability are Z-6020, Z-6030, Z-6032, Z-6040, Z-6075,and Z-6076 available from Dow Corning Corporation, Midland, Mich.Suitable precision glass microbead spacers are available in anassortment of sizes from Duke Scientific, Palo Alto, Calif.

[0046] Transparent electrodes 116 and 118, which may be any materialwhich bonds well to second substrate 112, are resistant to corrosion toany materials within the electrochromic device, resistant to corrosionby the atmosphere, have minimal diffuse or specular reflectance, highlight transmission, near neutral coloration, and good electricalconductance. Transparent electrodes 116 and 118 may be fluorine-dopedtin oxide, doped zinc oxide, zinc-doped indium oxide, tin-doped indiumoxide (ITO), ITO/metal/ITO (IMI) as disclosed in “Transparent ConductiveMultilayer-Systems for FPD Applications,” by J. Stollenwerk, B. Ocker,K. H. Kretschmer of LEYBOLD AG, Alzenau, Germany, the materialsdescribed in above-referenced U.S. Pat. No. 5,202,787, such as TEC 20 orTEC 15, available from Libbey Owens-Ford Co. of Toledo, Ohio, or othertransparent conductors. Generally, the conductance of transparentelectrodes 116 and 118 will depend on their thickness and composition.IMI generally has superior conductivity compared with the othermaterials. IMI is, however, known to undergo more rapid environmentaldegradation and suffer from interlayer delamination. The thickness ofthe various layers in the IMI structure may vary, but generally thethickness of the first ITO layer ranges from about 10 ∪ to about 200 ∪,the metal ranges from about 10 ∪ to about 200 ∪, and the second layer ofITO ranges from about 10 ∪ to about 200 ∪. If desired, an optional layeror layers of a color suppression material 130 may be deposited betweentransparent electrodes 116 and 118 and the inner surface 112 b ofsubstrate 112 to suppress the transmission of any unwanted portions ofthe electromagnetic spectrum.

[0047] To form the electrode pattern shown in FIG. 3, an entire layer oftransparent electrically conductive material may be formed on surface112 b of substrate 112 through known techniques such as sputtering,evaporating, and chemical vapor deposition, and the like, and then theregions thereof corresponding to gap 117 may be removed by etching, suchas chemical, laser, or mechanical etching. Alternatively, the patternmay be formed using photolithography, ink jet printing, contactprinting, or any other manner known in the art.

[0048] When the interdigitated fingers 116 a and 118 a of electrodes 116and 118, respectively, are of equal width, the electrochromic devicetends to exhibit stripes of alternating color when in a lowtransmittance state. These stripes are caused by the co-planar relationof the electrodes and by the anodic and cathodic species inelectrochromic medium 124 migrating towards the respective electrodesand donating or accepting electrodes and entering their colored statesin close proximity to the surfaces of the electrodes. To reduce thiseffect, the width of the electrode fingers may be decreased, while thenumber of such fingers may be increased.

[0049] To further reduce the visibility of any such striping, the widthof the fingers of one electrode may be increased while decreasing thewidth of the fingers of the other electrode. An example of such anarrangement is shown in FIG. 3. In the example shown, the width offingers 116 a of first electrode 116, which serves as the cathode, isfive times wider than fingers 118 a of second electrode 118, whichserves as the anode. Thus, the ratio of the widths of the fingers offirst electrode 116 to the widths of the fingers of the second electrode118 would be 5:1. Because the surface area of one electrode would thusbe five times greater than the surface area of the second electrode,anodic and cathodic species in electrochromic medium 124 would notbecome reduced or oxidized at the same rates if provided in equalquantities in the electrochromic medium. If the cathode has the largersurface area, the amount of anodic species may be correspondinglyincreased so as to increase the rate at which the anodic speciesoxidizes within chamber 122. As is well known in the field ofelectrochemistry, the current due to an electrochemical process isrelated to the electrode area and the concentrations and diffusioncoefficients of the electroactive components. Commonly assigned U.S.Pat. No. 6,137,620, entitled “ELECTROCHROMIC MEDIUM WITH CONCENTRATIONENHANCED STABILITY, PROCESS FOR PREPARATION THEREOF AND USE INELECTROCHROMIC DEVICES,” filed on Apr. 30, 1999, by T. Guarr et al.,teaches the concept of adjusting the concentrations of the anodic andcathodic materials for optimal device operation. The disclosure of U.S.Pat. No. 6,137,620 is incorporated in its entirety herein by reference.Preferably, the electrochromic medium 124 is adjusted to reflect thechanges in electrode area, i.e., a ratio of electrode surface area of1:2 anode to cathode would result in a ratio of 2:1 anodic to cathodicspecies change from equal area electrode concentrations. The ratio ofanode to cathode surface area and the ratio of cathodic to anodicspecies are preferably between 20:1 to 1:20, more preferably between10:1 to 1:10, and even more preferably between 5:1 to 1:5.

[0050] Another approach for eliminating or reducing the visibility ofany striping is to utilize anodic and cathodic species exhibitingsimilar color transitions. U.S. Pat. No. 6,020,987, entitled“ELECTROCHROMIC MEDIUM CAPABLE OF PRODUCING PRE-SELECTED COLOR,” filedon Apr. 2, 1997, by K. L. Baumann et al. discloses the selection ofelectroactive components for an electrochromic mirror so as to obtain aperceived color. The disclosure of U.S. Pat. No. 6,020,987 isincorporated in its entirety herein by reference. One example of anelectrochromic medium having anodic and cathodic species exhibitingsimilar color transitions includes a solution oftetra(N-methyl)-p-phenylenediamine (TMPD) and1,1′-dimethyl-4,4′-bipyridinium bis(tetrafluoroborate) (28 mM each) inpropylene carbonate. An electrochromic cell was constructed by creatingtwo electrically isolated conductive areas on a single ITO-coated glasssubstrate using laser patterning. The patterning consisted of etching anapproximately 100 μm wide isolation line in a serpentine arrangement toprovide a pair of interdigitated electrodes whose fingers were roughly2500 μm across. The electrochromic cell was otherwise fabricated inconventional fashion, utilizing the patterned ITO-coated glass substrateas a first substrate, an unpatterned ITO-coated glass plate as a secondsubstrate, and an epoxy seal around the periphery between the twosubstrates to provide a cell spacing of approximately 137 μm. The cellwas filled using a vacuum backfilling technique with the aboveelectrochromic solution. Electrical connection was made to bothelectrodes of the first substrate (no electrical connection was made tothe second, unpatterned substrate). Upon application of 1.2 V DC, thedevice achieved a fairly blue uniform coloration. The color thatdeveloped at the anode was slightly more purple that the royal bluecolor observed at the cathode.

[0051] According to a second example, an electrochromic cell wasfabricated in the same manner as the above example except that the widthof the interdigitated electrode fingers was approximately 5 mm. Thedevice was then filled with a solution of 30 mM5,10-dimethyl-5,10-dihydrophenazine, 30 mMbis(3,5-dimethylphenyl)-4,4′-bipyridinium bis(tetrafluoroborate), 30 mMTinuvin P, and 3% PMMA in propylene carbonate. Upon application of 1.2 VDC, the device achieved a fairly uniform green coloration. The color atthe anode was somewhat less intense than the color developed at thecathode.

[0052] Although the colors developing at the anode and the cathode inthe above examples were not matched exactly, the closeness of thecoloration at the anode and the cathode is sufficient to substantiallyreduce or eliminate the perceivable striping.

[0053] Depending upon the window application, it may also be possible toprovide a diffuser on or in the window so as to effectively blur anystriping that would otherwise be visible. For example, such a diffusermay be used for skylights incorporating the present invention. If adiffuser layer is utilized, it is preferably provided on a surface ofthe electrochromic window that is closest to the viewer. Alternatively,the surface of the window closest to the viewer may be roughened so asto provide a diffuser directly in the surface on the electrochromicdevice.

[0054] It should be noted that the electrode pattern illustrated inFIGS. 3 through 5 is not drawn to scale, but is enlarged to more clearlyillustrate the concepts of the present invention. For a 5:1 electrodesurface area ratio, the width of the electrode fingers 116 a and 116 bis preferably sufficient to provide the selected ratio while providing agap 117 between the electrodes of sufficient width so as to electricallyisolate the electrodes from one another. The thickness of electrodes 116and 118 is preferably sufficient to provide a sheet resistivity ofpreferably less than about 100 Ω/□, more preferably less than about 40Ω/□, and even more preferably less than about 20 Ω/□. Clearly, theelectrodes may have various dimensions, particularly when ratios of 10:1or even 20:1 are used and the electrode patterns are not limited to thespecific pattern illustrated in FIG. 3. Thus, first and secondelectrodes 116 and 118 may have any pattern, provided they areelectrically separated from one another. Preferably, the patternutilized provides for perceived uniform coloring of the electrochromicmedium. It should also be noted that the perceived visibility of anystriping will depend upon the electrode finger widths relative to thedistance a viewer is from the electrochromic window as well as the colorseparation of the anodic and cathodic species. For example, a skylightor a window mounted high above the floor may not exhibit striping whilea window having the same electrode finger widths that is located whereviewers may closely approach the window may exhibit more considerablestriping. Thus, it will be appreciated that the width of the electrodefingers may vary considerably.

[0055] By providing both electrodes 116 and 118 on the inner surface ofa single substrate, all the coloration of the anodic and cathodicspecies occurs at (or near) the surface on which electrodes 116 and 118are provided. Thus, any UV radiation entering chamber 122 via substrate114 may be absorbed by a UV absorbing material provided in chamber 122before the UV radiation reaches the colored anodic and cathodic speciesof the electrochromic material. Thus, the UV absorbing material is muchmore effective, and the electrochromic device will exhibit a muchgreater lifetime. To further reduce the possibility that UV radiationmay reach the colored species in electrochromic material 124, a UVreflective or absorbing material or film stack may be applied to outersurface 114 a or inner surface 114 b of substrate 114.

[0056] Another advantage to providing both the first and secondelectrodes on a single surface of one of the substrates is that thiselectrode configuration enables the electrochromic device to be operatedat a much lower current. Prior constructions, such as that shown in FIG.1, may draw around 50 to 60 mA when a potential of 1.0 to 1.2 volts isapplied between the electrodes. This current varies based on the size ofthe electrochromic device as well as other parameters such as theconcentrations and diffusion coefficients of the electroactivematerials. By placing both electrodes on a single surface, anelectrochromic device may be constructed that draws as little as 2 mAwhen a potential of 1.0 to 1.2 volts is applied between the electrodes.Such a reduction in the current draw represents a very significantimprovement, particularly when such a structure is implemented in thearchitectural windows of a large building.

[0057] In addition to the advantages noted above, providing bothelectrodes on a single surface of a single substrate also provides for ahigher tolerance level for substrates having surfaces that are notperfectly smooth or flat. Thus, tempered glass may be used as one orboth of the substrates without adversely affecting the spacings betweenthe electrodes. Yet another advantage to providing both the electrodeson the surface of a single substrate is that the other substrate neednot be selected of materials that are conducive to the deposition ofelectrode materials. Thus, substrate 114 may be formed of a wide varietyof materials, such as plastic.

[0058] Further, because only one of the substrates needs to be coatedwith the electrode material, the cost for producing the electrochromicdevice may be reduced. Also, the distance between substrates 114 and 112becomes less critical and the substrates may be spaced closer together,thereby reducing the overall thickness of the electrochromic device anddecreasing the amount of materials required to fill chamber 122.Additionally, the electrode arrangement provides for less segregation ofthe electroactive materials in electrochromic medium 124 than is presentin devices having conventional electrode arrangements.

[0059]FIGS. 6 through 9 show an electrochromic device 200 constructed inaccordance with a second embodiment of the present invention. Like thefirst embodiment, the second embodiment provides both first and secondelectrodes carried on the inner surface of substrate 112. Unlike thefirst embodiment, however, first and second electrodes 216 and 218 arenot disposed in a coplanar manner on inner surface 112 b, but rather arearranged in a stacked configuration. To prevent electrical shorting, adielectric or other insulating layer 220 is provided between electrodes216 and 218. To allow the electrochromic medium to come into contactwith electrode 216, a plurality of apertures 225 such as pores and/orperforations are made through both electrode 218 and dielectric layer220. The apertures in electrode 218 and the apertures in layer 220 arein communication with one another so that the electrochromic medium mayfill perforations 225 and reach portions of electrode 216.

[0060] Layers 216, 218, and 220 may be formed on surface 112 b ofsubstrate 112 by photolithography, screen or ink jet printing ofdielectric and conductive inks, providing continuous coatings of eachlayer and then utilizing laser ablation to form the perforations throughthe top two layers of the stack, sputtering the materials onto thesubstrate through a mask or sputtering onto a continuous conductor layerhaving a perforated insulator stack already provided thereon, chemicalvapor deposition, or by laser-assisted chemical deposition. Dependingupon the size spacing, number of apertures 225, and the thicknesses ofelectrode 218 and dielectric layer 220, the ratio of the exposed surfaceareas of the two electrodes may fall in the range of 10:1 to 1:10. Asdiscussed above, the ratio of anodic to cathodic species in theelectrochromic medium may be varied to compensate for the variation inexposed electrode surface areas. For example, apertures 225 may have adiameter of 1 mm and be formed 250 μm apart in a close-packed repetitivepattern. The dimensions of electrode layers 216 and 218 are selected toobtain a sheet resistivity of preferably less than about 100 Ω/□, morepreferably less than about 40 Ω/□, and even more preferably less thanabout 20 Ω/□, and the thickness of dielectric layer 220 is selected toprovide enough electrical isolation between the electrodes. Electrodelayers 216 and 218 may be formed of any conventional electricallytransparent material commonly used in such electrochromic devices, whiledielectric layer 220 may be formed of any transparent dielectricmaterial and is preferably formed of silicon dioxide, zinc oxide, andother materials known in the art due to their inert characteristicsrelative to the electrochromic material. Dielectric layer 220 may alsobe formed using an adhesive used to attach electrode layer 218 toelectrode layer 216 or may be formed of a porous material such that itspores function as apertures 225.

[0061]FIGS. 10 and 11 show an electrochromic device 300 constructed inaccordance with a third embodiment of the present invention.Electrochromic device 300 differs from electrochromic device 200 in thatelectrode layer 218 is replaced with a layer of a fine metal mesh 318.Mesh layer 318 is formed of nickel, gold, INCONEL®, copper, etc. withsufficiently fine strands so as to not adversely affect the image viewedthrough the electrochromic device. Dielectric layer 220 may be formed ofany porous transparent dielectric material and need not haveperforations that are registered with any openings in the mesh layer318. Thus, dielectric layer 220 may be formed using a NUCLEPORE®membrane available from Corning Incorporated of Corning, N.Y.

[0062] Electrochromic devices 200 and 300 of the second and thirdembodiments provide much of the same advantages as the first embodiment.Unlike the conventional electrochromic device shown in FIG. 2, theelectrochromic material is not solely confined between the two electrodelayers along the sight line of a person looking through the device.Thus, the second and third embodiments of the present invention allowfor use of a solution-phase electrochromic material or even a hybridsystem incorporating a solid-state electrochromic material andsolution-phase electrolyte.

[0063] While a specific structure is shown in the drawings and describedabove, it will be appreciated by those skilled in the art that theinventive electrode design may be incorporated in windows and otherdevices having different structures. For example, an electrochromicwindow incorporating the inventive electrode design could be constructedthat also incorporates a photovoltaic device to provide power to theelectrochromic window. The disclosure of commonly assigned U.S. Pat. No.6,045,643, entitled “ELECTRO-OPTIC WINDOW INCORPORATING A DISCRETEPHOTOVOLTAIC DEVICE AND APPARATUS FOR MAKING SAME,” filed on Jan. 26,1996, by Harlan Byker et al., is incorporated by reference herein.

[0064] Although the above invention has been described with reference touse in an architectural window, it will be appreciated by those skilledin the art that the above constructions could similarly be used in anelectrochromic mirror, such as the type used for rearview mirrors in avehicle. To construct the device as a mirror, a reflective layer couldbe applied to outer surface 112 a of substrate 112, or the electrodescould be formed with a reflective and electrically conductive material.Alternatively, transparent electrodes could be formed over or under ametallic reflective coating.

[0065] An electrochromic device using a component including theelectrode design of the present invention can be easily made part of aninsulated glass (IG) unit. As shown in FIGS. 12A and 12B, an IG unit 400typically has two panes of glass 402 and 404 sealably bonded together inspaced-apart relation to define a chamber therebetween. IG unit 400further includes a layer of low heat conducting gas 406, such as argon,in the chamber. As shown in FIG. 12A, an electrochromic device 407 canbe incorporated by applying a substrate 410 carrying first and secondelectrodes 412 and 414, respectively, and an electrochromic medium 408to one of panes 402 and 404. First and second electrodes 412 and 414include first surfaces 412 a and 414 a facing substrate 410, and secondsurfaces 412 b and 414 b opposite the first surfaces. Electrochromicmedium 408 is disposed over the second surfaces of first and secondelectrodes 412 and 414 in electrical contact therewith. In addition tosubstrate 410, electrochromic device 407 may include a second substrate411 provided to keep separation between electrochromic medium 408 andthe low heat conducting gas 406 or to maintain a solution-phaseelectrochromic medium in a chamber formed between substrates 410 and411.

[0066] Alternatively, as shown in FIG. 12B, the electrode design couldbe incorporated into one of the panes and the electrochromic medium isdisposed thereon. Insulated units can further carry additional layers416 and 418 such as UV absorbing/blocking layers, an IRreflecting/blocking layer, a low-E layer, a third pane, etc. Layers 416and 418 may be carried on a front surface 402 a or rear surface 402 b ofglass 402 or on a front surface 411 a or rear surface 411 b of secondsubstrate 411. Layers 416 and 418 may be carried on the same surface oron different surfaces of the same or different elements. Electrochromicmaterials exhibiting near infrared absorbence as is described in U.S.Pat. No. 6,193,912 are especially useful in devices in windows of thisdesign. The entire disclosure of U.S. Pat. No. 6,193,912 is incorporatedherein by reference.

[0067] The above description is considered that of the preferredembodiments only. Modifications of the invention will occur to thoseskilled in the art and to those who make or use the invention.Therefore, it is understood that the embodiments shown in the drawingsand described above are merely for illustrative purposes and notintended to limit the scope of the invention, which is defined by thefollowing claims as interpreted according to the principles of patentlaw, including the doctrine of equivalents.

The invention claimed is:
 1. An electrochromic device comprising: atransparent first substrate having an outer surface and an innersurface; a second substrate having an inner surface spaced apart fromsaid inner surface of said first substrate; a perimeter seal, which,with said inner surfaces of said first and second substrates, defines achamber therebetween; a first electrode carried on said inner surface ofsaid second substrate; a second electrode also carried on said innersurface of said second substrate, said second electrode beingelectrically isolated from said first electrode; a UV radiationattenuating material associated with said device; and an electrochromicmedium disposed in said chamber between said inner surface of said firstsubstrate and said inner surface of said second substrate, wherein saidUV radiation attenuating material reduces the amount of UV radiationimpacting a portion of said electrochromic medium.
 2. The electrochromicdevice of claim 1, wherein said UV radiation attenuating material isprovided in said chamber.
 3. The electrochromic device of claim 1,wherein said UV radiation attenuating material is provided on a surfaceof said first substrate.
 4. The electrochromic device of claim 3,wherein said UV radiation attenuating material is provided in a filmapplied to a surface of said first substrate.
 5. The electrochromicdevice of claim 1, wherein said first and second electrodes aresubstantially coplanar.
 6. The electrochromic device of claim 1, whereinsaid electrochromic medium includes cathodic and anodic species, whereinthe ratio of cathodic to anodic species within said electrochromicmedium is a function of the ratio of the surface areas of said firstelectrode and said second electrode.
 7. The electrochromic device ofclaim 1, wherein said electrochromic medium includes anodic and cathodicspecies exhibiting substantially similar color transitions.
 8. Theelectrochromic device of claim 1, wherein said electrochromic device isa mirror.
 9. A window comprising the electrochromic device of claim 1.10. The window of claim 9 and further including a window pane, whereinsaid UV attenuating material is carried on a surface of said windowpane.
 11. An electrochromic device comprising: a transparent firstsubstrate having an outer surface and an inner surface; a secondsubstrate having an inner surface spaced apart from said inner surfaceof said first substrate; a perimeter seal, which, with said innersurfaces of said first and second substrates, defines a chambertherebetween; a first electrode carried on said inner surface of saidsecond substrate; a second electrode also carried on said inner surfaceof said second substrate, said second electrode being electricallyisolated from said first electrode, wherein said second electrodecomprises a series of conductive members that are electrically isolatedfrom one another; and an electrochromic medium disposed in said chamberbetween said inner surface of said first substrate and said innersurface of said second substrate.
 12. The electrochromic device of claim11, wherein said second electrode further comprising a contact stripelectrically coupled to each of said series of conductive members. 13.The electrochromic device of claim 11 and further including a UVattenuator associated with said device.
 14. The electrochromic device ofclaim 11, wherein said first and second electrodes are substantiallycoplanar.
 15. The electrochromic device of claim 11, wherein saidelectrochromic medium includes cathodic and anodic species, wherein theratio of cathodic to anodic species within said electrochromic medium isa function of the ratio of the surface areas of said first electrode andsaid second electrode.
 16. The electrochromic device of claim 11,wherein said electrochromic medium includes anodic and cathodic speciesexhibiting substantially similar color transitions.
 17. An insulatedglass window comprising: a first glass pane; a second glass panesealably bonded to said first glass pane to define a chambertherebetween; a low heat conducting gas provided in said chamber; and anelectrochromic device disposed within said chamber, said electrochromicdevice comprising: first and second electrodes carried on a singlesurface of a substrate, said first and second electrodes beingelectrically isolated from one another, each electrode having a firstsurface facing the substrate, and a second surface opposite said firstsurface; and an electrochromic medium in electrical contact with saidfirst and second electrodes.
 18. The insulated glass window of claim 17,wherein said second glass pane functions as said substrate.
 19. Theinsulated glass window of claim 17, wherein said electrochromic elementincludes a second substrate spaced apart from the other substrate,which, with a seal, defines a sealed second chamber therebetween, saidelectrochromic medium being disposed in said second chamber.
 20. Theinsulated glass window of claim 19, wherein said second substrate isspaced apart from said first and second glass panes.
 21. The insulatedglass window of claim 17, wherein said electrochromic medium is disposedover said second surfaces of said first and second electrodes.
 22. Theinsulated glass window of claim 17, wherein said substrate is attachedto a surface of one of said first and second glass panes within saidchamber.
 23. The insulated glass window of claim 17 and furtherincluding an ultraviolet attenuator carried on a surface of one of saidfirst glass pane and said electrochromic device.
 24. An electrochromicmirror comprising: a transparent first substrate having an outer surfaceand an inner surface; a second substrate having an inner surface spacedapart from said inner surface of said first substrate, which, with aseal, defines a chamber therebetween; a first electrode carried on saidinner surface of said second substrate; a second electrode also carriedon said inner surface of said second substrate, said second electrodebeing electrically isolated from said first electrode; an electrochromicmedium disposed in said chamber between said inner surface of said firstsubstrate and said inner surface of said second substrate, which carriessaid first and second electrodes; and a reflector provided on a surfaceof said second substrate.
 25. The electrochromic mirror of claim 24,wherein said reflector is provided on said inner surface of said secondsubstrate.
 26. The electrochromic mirror of claim 25, wherein saidreflector includes an electrically conductive layer that functions assaid second electrode.
 27. The electrochromic mirror of claim 24,wherein said reflector is provided on an outer surface of said secondsubstrate.